1. Field of the Invention
The prsent invention relates to a method of manufacturing printed circuit boards.
2. Description of the Prior Art
A prior art printed circuit resin board having at least one circuit layer formed on the resin board is already known. As the miniaturization of electronic systems progress, however, a growing density of components mounted on the printed circuit board increases the heat generated from these mounted components. A resulting problem to be solved is the deteriorating performance of these mounted components due to a higher temperature in the adjacent area of the printed circuit resin board as a result of an insufficient heat releasing capacity of these printed circuit resin boards. To cope with this, components provided with radiation fins have been mounted, but a drawback was a higher cost of mounted components. As the number of mounted components increases, the printed circuit board arches slightly due to a lesser flexural rigidity of the printed circuit resin board, which makes it impossible to be incorporated in the electronic system. Even if it could be incorporated, it comes in contact with neighboring printed circuit boards and occasionally seriously jeopardizes the circuit function. Moreover, generation of noise cannot be avoided, as the printed circuit resin board has a poor shielding effect.
Therefore, offered in U.S. patent application Ser. No. 691,611, is a printed circuit board in which a metal board and a resin board are glued together by means of a bonding sheet, holes which are filled with resin are provided on the metal board, lead wire holes are provided at the centers of the resin filled the holes, and at least one circuit layer and through holes are formed on the resin board.
In this printed circuit board, its better heat releasing capacity facilitates a higher density of mounted components, while there is no deterioration in the functions of the mounted components even though the heat value generated from the mounted components is greater, and costly mounted components with radiation fins and the like are unnecessary. Also its greater flexural rigidity gives no chance of arching to the printed circuit board even if the number of the mounted components increases, so that insertion of the printed circuit board into the electronic system can be made with much ease, and the inserted printed circuit board does not come into contact with neighboring printed circuit boards. Further, its better shielding effect facilitates prevention of noises. Therefore, it is possible to widely expand the applicable scope of printed circuit boards.
Following is an explanation of the conventional method of manufacturing such printed circuit boards hereinafter. First, holes are provided on a metal board material, resin is filled into the holes, the resin is then hardened, lead wire holes are provided at the centers of the resin filled holes, a resin board material having at least one circuit layer and through holes thereon is glued to the metal board material by means of a bonding sheet, and finally printed circuit boards are made from the the metal board material being and the resin board material glued together and by finishing their outer configurations.
In present methods of manufacturing printed circuit boards, which requires filling resin into the holes of each metal board and further hardening the resin, the manufacturing operation is troublesome and long while the productivity is rather poor.